The studies proposed in this new SPORE project are designed to provide strong rationale for a vitamin D3- based approach to lung cancer prevention. We recently demonstrated that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the active metabolite of vitamin 03, significantly inhibits the growth of lung cancer cells and antagonizes nuclear factor-KB (NF-KB) action. NF-KB signaling plays a key role in inflammation, and has been shown to underlie smoking-associated lung inflammation and carcinogenesis. Together, this suggests that 1,25(OH)2D3 may be useful for chemoprevention of lung cancer. Because systemic 1,25(OH)2D3 administration is complicated by its hypercalcemia-inducing properties, we propose to use oral supplementation with vitamin D3 to safely achieve chemopreventive1,25(OH)2D3 levels within lung tissues. Upon ingestion, vitamin D3 is readily converted to the non-toxic circulating precursor, 25(OH)D3, which is subsequently converted to 1,25(OH)2D3 within the lung by CYP27B1-expressing bronchial epithelial cells and alveolar macrophages. To determine the impact of vitamin D3 exposure on pulmonary inflammation and lung cancer risk we will: (Aim 1) utilize samples and data from 548 cases from our SPORE Lung Tumor Registry, and 180 cases and 993 controls from the Pittsburgh Lung Screening Study (PLuSS) to evaluate the relationship between variation in vitamin D3 and NF-KB pathway genes, 25(OH)D3 serum levels, and risk of lung cancer; (Aim 2) use banked samples from 150 PLuSS participants to establish the association between 25(OH)D3 serum levels and inflammation and lung cancer risk biomarkers in sputum; (Aim 3) use murine models to quantify the effects of vitamin D3 status on NNK-induced lung carcinogenesis and cigarette smoke-induced pulmonary inflammation, and examine the impact of cigarette smoke exposure on 25(OH)D3 levels and expression of vitamin D3-metabolizing enzymes; and, (Aim 4) conduct a bioeffectiveness study of vitamin D3 supplementation in individuals at increased risk for lung cancer. We will evaluate whether supplementation corrects vitamin D3 deficiency and also investigate effects on inflammation and lung cancer risk biomarkers in sputum, circulating inflammation markers, and pulmonary function in this aim.